ABSTRACTAs with many heat exchangers, nuclear steam generators are subject to the accumulation of corrosion product deposits on heated tube surfaces and other internal components on the secondary (shell) side. These deposits can have adverse effects on thermal efficiency, material integrity, and in some cases plant operability. Accordingly, plant operators routinely devote substantial resources to limiting the generation and accumulation of deposits, including periodic removal of deposits through various mechanical and chemical approaches. Since the 1980s, chemical cleaning processes with solvents designed to remove all (or nearly all) of the iron- and copper-based deposit material from the steam generator (SG) secondary side have been employed in dozens of different units worldwide. Although these full-bundle “hard” chemical cleaning processes have generally been quite successful in removing large fractions of the deposit mass (typically >95%), they are complex, costly evolutions that require additional plant downtime. Additionally, a few units have unexpectedly experienced declines in SG heat-transfer efficiency and plant production following a successful cleaning application due to the removal of thermally beneficial scale layers.During the past 15 years, alternative processes designed to periodically remove only a fraction of the secondary SG deposit inventory have been developed and qualified by the authors. One of these is an advanced scale conditioning agent (ASCA) treatment, a dilute or “soft” chemical cleaning method that focuses on penetrating through consolidated tube scale layers. By removing a fraction of the iron- based matrix material throughout the scale layer thickness—but without fully removing the layer— ASCA applications increase the average scale porosity and thereby improve the associated scale thermal properties, raising SG thermal performance levels. ASCA processes have three principal benefits: 1) immediate, reliable improvements in SG heat-transfer efficiency as demonstrated by analysis of more than a dozen field applications, 2) reduction in the long-term rate of deposit accumulation within the SG (lowering long-term risks of component corrosion and heat-transfer fouling), and 3) substantially reduced application complexity and cost, including no added plant downtime.
ABSTRACTTraditional water treatment methods pose several challenges to large-vessel preservation. The economics of continuous dosing and environmental restrictions concerning the disposal of treated water need to be considered. One solution to these challenges involves the application of an immiscible corrosion inhibiting oil partition on the water surface (henceforth referred to as a “float coat”). This paper will highlight challenges of traditional preservation methods and examine the efficacy of one commercial float coat (henceforth referred to as “Product A”).INTRODUCTIONLarge vessel preservation is typically accomplished through one of two methods: chemical treatment of water during hydrotesting or heavy-duty epoxy coating systems. These treatment systems have proven to be effective. However, novel approaches to large vessel preservation provide an opportunity to overcome challenges involved with more traditional preservation methods.Chemical TreatmentAboveground storage tanks (ASTs) in the petroleum industry come in a wide variety of sizes, ranging from modest sizes of 200 m3 up to storage volumes in excess of 100,000 m3, 1. For even the most modest dosage rates of chemical treatment at 500 ppm, costs can exceed to $2.5 million for more than 115 m3 of chemical treatment.CoatingsCoatings can be separated into removable, or “temporary” coatings, and permanent coatings. After the application of either type of coating, the proper amount of cure time must be allowed for the coating to achieve peak performance. Typical recommendations call for one week of cure time. During this time, no maintenance or testing can be performed on coated areas, resulting in lost time and productivity.For tanks with a 91.4 m diameter and 18.3 m wall height1, the total wall surface area is approximately 5300 m2. Given a spread rate of 3.7 m2 per liter, over 1500 liters of the coating are required, costing upwards of $40,000 USD. While removable or temporary coatings typically cost less than permanent coatings, the reapplication of any coating for long term preservation would require significant labor cost for surface preparation and application. Finally, lost time (for product application and cure time) is also a considerable factor resulting in lost profits.
Clark, Brandi N. (National Institute of Standards and Technology) | Rentz, Ross (National Institute of Standards and Technology) | McColskey, J. David (National Institute of Standards and Technology) | Sowards, Jeffrey W. (National Institute of Standards and Technology)
ABSTRACTNACE TM0177 Method B is a standard method for evaluating stress-corrosion cracking (SCC) resistance. To conduct the test, a beam of material is loaded into a three-point bend fixture and exposed to the specified test solution, then inspected for cracking (failure) at predetermined time intervals. The three-point bending equation is used to calculate peak stress in the center of the beam; however, the bend equation is only valid for elastic deformation. In actuality, the specimens have a pair of holes drilled at the centerline to act as stress concentrators, resulting in stresses that are both elastic and plastic as well as a non-uniform stress distribution near the holes. As a result, the reported critical stress (SC) obtained from Method B is a “pseudo-stress” rather than a true stress. In this study, Digital Image Correlation (DIC) was used to determine the actual strain distributions over the surface of the bend samples made from a representative mix of both corrosion-resistant alloys (Type 316, 2205, 420, and 440 stainless steels) and pipeline steels (API 5L X65 and X80) and compare the measured peak stress to the pseudo-stress calculated using Method B. The measured average stress concentration factor due to the holes was 1.74 ± 0.20, which was in very good agreement with theoretical predictions. To increase the accuracy of Method B, future revisions to the standard should consider modifying the calculation of pseudo-stress to account for this stress concentration factor.INTRODUCTIONIn most applications, as the alloys used become more resistant to general corrosion, they tend to become more susceptible to localized forms of attack, including stress corrosion cracking (SCC) and sulfide stress cracking (SSC).1-3 These forms of damage are a result of a susceptible material being simultaneously exposed to tensile stress and corrosive environment. Classical examples of material/environment combinations resulting in SCC are ferritic steels exposed to hydroxides or nitrates, brasses exposed to ammonia environments, and austenitic stainless steels exposed to chlorides; however, recent experience has demonstrated that a wide range of previously unreported material-environment combinations can result in SCC.1, 4 SSC is a special case of SCC where hydrogen sulfide (H2S) is the corrodent involved in the cracking mechanism. In order to avoid SCC in practice, sound test methods are needed to screen for susceptible material-environment combinations. Ideally, the result of these methods is a critical stress above which a material is susceptible to SCC in the given environment that can be used to make design decisions.5
Permeh, Samanbar (Florida International University) | Reid, Carla (Florida International University) | Echeverría Boan, Mayrén (Florida International University) | Lau, Kingsley (Florida International University) | Tansel, Berrin (Florida International University) | Duncan, Matthew (State Materials Office) | Lasa, Ivan (State Materials Office)
ABSTRACTMicrobiologically Influenced Corrosion (MIC) occurs in environments where microbial attachment and biofilm formation occurs. The microbial metabolic activities which cause MIC affect materials in a wide variety of industries. Although MIC has not traditionally been a major durability concern for Florida coastal and inland bridges, a recent finding by the Florida Department of Transportation (FDOT) of severe corrosion of steel bridge piles with strong evidence of microbial activity, has motivated the present study. As a preliminary research, identify the possible susceptibility of a case study marine bridge infrastructure to MIC is the main objective. This will be supported by determining the bacteria, nutrient levels, environmental conditions and other factors that could support MIC. A site visit to a bridge was carried out in 2016 and water samples (close to the site) at varying depths, as well as underwater pictures of the bridge steel piles were taken. The chemical composition including pH, total organic nitrogen, nitrate, phosphate, sulfate, chloride, ammonia and microbiological content of the samples were determined. Sulfate Reducing Bacteria (SRB), Slime Forming Bacteria (SFB), Iron Reducing Bacteria (IRB), and Acid Producing Bacteria (APB) were found in water samples. The presence of carbon, sulfate, nitrogen, phosphorus, as well as Ca, K, Na, Mg in water samples of the case study could provide the necessary nutrient to support large bacteria colonization. Site visit results (water chemistry and microorganism content) were compared with database information of water management districts of Florida, in order to find similar conditions that could support MIC. As a result, many sites with similar characteristics as the case study were found that may support MIC.INTRODUCTIONMicrobiologically Influenced Corrosion (MIC) is an important degradation mechanism for materials in a wide variety of industries. Although MIC has not traditionally been a major durability concern for Florida coastal and inland bridges, a recent finding in Florida showed severe corrosion of submerged steel bridge piles (with evidence of microbial activity), which has motivated the present research. Diagnostic evaluation is considered as the first step in determining if corrosion problems are related to MIC. An accurate diagnosis should determine the severity of the problem and if microorganisms have influence on it. This is also supported by an assessment stage, which includes collecting information of the history of the system (corrosion monitoring activities, repair records, water chemistry records, operating environment, etc.), taking samples of the microorganisms (in water and in biofilm), analyzing water chemistry and conducting visual inspection of the system.1 The objective of the preliminary study in progress is to identify the possible susceptibility of bridge steel piles in Florida waters to degradation associated with microorganisms. Early observations from a case study of a Florida marine bridge as well as identification of similar environmental conditions in Florida are presented in order to provide a broader perspective of actual field conditions. The collected information on the bacteria count, nutrient levels, environmental conditions and other factors that provide insight on the contributing factors to MIC will be considered in the development of upcoming laboratory and field research to identify corrosion mechanisms. Furthermore, identification of possible sites in Florida that may be susceptible to this type of corrosion is important so that future resources for mitigation can be appropriated. In the cursory review presented here, a literature review of MIC for steel in marine environment is summarized, followed by presentation of the case study and a review and comparison of pertinent environmental conditions from available environmental databases for Florida water bodies.
ABSTRACTAccelerated corrosion testing is an important tool for understanding the corrosion behavior of aerospace alloys, but many standardized accelerated tests do not correlate well with seacoast exposures, and results can be drastically different from test-to-test. Previous testing of aluminum lithium alloy 2060 has shown that DB ASTM G85-A2 correctly distinguishes between exfoliation susceptible and resistant tempers. In the current study, in-situ measurements were used to deconstruct the testing environment of DB ASTM G85-A2 to provide an understanding of what makes this test successful when others are not. Time of wetness measurements showed that complete drying of the sensor did not occur until 1.5 - 4 hours after the dry air purge began. After 2 days, the open circuit potential of AA2060 was stable during the salt spray cycle and decreased during the dry cycle. After longer testing time (8 days), the potential was lower, due to activation of more localized corrosion sites. In addition, a peak in potential was observed at around 10 minutes into the dry air purge after 8 days of testing. This change in potential was attributed to the impact of relative humidity on electrolyte film thickness and cathodic kinetics.INTRODUCTIONAccelerated laboratory testing is an important tool for understanding and predicting the corrosion behavior of aerospace alloys that are exposed to salt aerosols in the atmosphere during service. For accelerated testing to be useful, the results must correlate well with the corrosion behavior during service and be easily reproducible between different laboratories. Many standardized accelerated tests are currently used for high-strength aluminum alloys (ASTM standards G34, G85, G110, and B117), but these tests do not always correlate well with seacoast exposures and results can be drastically different from test-to-test. This disagreement limits accelerated testing utility and hampers alloy and temper development. The purpose of this study is to deconstruct accelerated testing mechanisms to understand why certain tests are successful and others are unsuccessful. This work will also provide a basis for improved accelerated test design.
ABSTRACTPBTC (2-phosphonobutane 1,2,4-tricarboxylic acid) has become the work horse for calcium carbonate scale inhibition in cooling water, water reuse, and water treatment applications operating at the edge of control technology. Economically, this stressed system inhibitor allows cooling tower operation at higher concentration ratios resulting in decreased water usage and discharge. The inhibitor also allows the reuse of water that would otherwise be discharged, possibly after costly treatment. It permits the use of less than desirable water in other applications.Performance and limits of this inhibitor were first characterized in a 1985 paper1. This paper expands these findings based upon over thirty years of field application and recent laboratory studies to elucidate behavior and performance of this “go to” inhibitor over a broad range of conditions. Test conditions simulated varied from easy to treat low concentration ratio HVAC towers, to water reuse applications, and into the range of hydrofracturing flow back brines.Data developed and reported includes inhibitor minimum effective dosage requirement as a function of saturation ratio (scaling index), temperature as it affects rate, residence time, and PBTC dissociation state. Performance as the sole inhibitor, and when applied with commonly used polymers, is also discussed.This paper stresses the upper limits for the inhibitor when used as the sole treatment, and in combination with other inhibitors. Both synergism and antagonism were observed for the inhibitor blends, with the interaction type being a function of ratio.Future reports will expand the PBTC performance data base to include calcium sulfate and barium sulfate scale control.INTRODUCTIONPBTC Models For Minimum Effective DosageExisting models for calculating the minimum effective dosage for scale control have been applied to industrial and oil field scale control treatment optimization since the 1970s. Standard correlations are routinely used in developing the models.1,2,3,4,5,6,7,8,9,10 The models typically apply to a single inhibitor. There is a driving force limit for each inhibitor, above which scale control cannot be achieved regardless of the inhibitor dosage. Knowing the upper limit is critical for selecting the optimum treatment program and in specifying control limits for a system such as an open recirculating cooling tower or membrane system. Limits for individual inhibitors have been well documented. Studies have been conducted to determine the impact of blending inhibitors on the upper driving force limit. Upper driving force limits' as expressed by calcite saturation ratio, were measured for calcium carbonate inhibition by individual inhibitors and combinations. Results were evaluated and blends were found to:
ABSTRACTThe potential of passive steel embedded in concrete is a key parameter on the value of the chloride corrosion threshold. The phenomenon of a potential-dependent chloride threshold (PDT) along with the corrosion macrocell coupling between active and passive steel assembly components allows to combine a corrosion initiation- propagation model to forecast the durability of reinforced concrete structures in marine service. Initial calculations using a one-dimensional and deterministic corrosion initiation-propagation model incorporating PDT resulted in lower damage development in an aged system than when using the traditional value of fixed chloride threshold (PIT) assumption. In contrast, for early stages of corrosion damage the relative effect tended to be in the opposite direction. These diverse outcomes are explained by the interplay between delayed corrosion initiation and concentration of corrosion when it is localized. An expansion of that PDT forecast model case is presented with emphasis on establishing the model output sensitivity to the choice of model input parameters, primarily to reveal the extent of the macrocell interaction between anodic and cathodic regions under various system conditions. The concrete parameters were: resistivity, oxygen diffusivity and chloride diffusivity, representing values comparable to those encountered in the field plus some extreme conditions, especially at the low resistivity end. A comparison with the traditional PIT approach was also examined.BACKGROUND AND INTRODUCTIONWhen modeling the durability of reinforced concrete structures, usually the corrosion initiation and the corrosion propagation stages are separately estimated. The mechanisms contributing to the respective corrosion process are commonly viewed as being isolated from one another.1 For instance; in the initiation stage the chloride-ion- penetration mechanisms (e.g. diffusional process) are frequently independent of the electrochemical processes taking place at the concrete-steel interface. However, research has shown that there is an increase of the chloride corrosion threshold value CT in cathodically polarized passive steel, delaying the initiation of corrosion.2-5 The effect may take place if corrosion has recently been initiated in a nearby region. Corrosion macrocell coupling can then depress the potential on the steel where corrosion has not yet started, with consequent increase the local value of CT. Thus, there is a coupling between the corrosion initiation and propagation processes. 2-5 Such effect can occur throughout a reinforced structure where the concrete cover thickness XC, diffusion coefficient D, surface chloride content CS, as well as the baseline value of CT vary from point to point.
Wang, Zhu (University of Science and Technology Beijing) | Tang, Xian (University of Science and Technology Beijing) | Xue, Junpeng (University of Science and Technology Beijing) | Zhang, Lei (University of Science and Technology Beijing) | Li, Ting (University of Science and Technology Beijing) | Lu, Minxu (University of Science and Technology Beijing)
ABSTRACTWith increasing concerns of air pollution, the emission of sulfur from industries in the form of SOx has been closely monitored and regulated by many countries. Technological and industrial efforts have been taken in the past several decades and many clean-up methods have been developed. However, corrosion, especially pitting and stress corrosion cracking, has been reported previously under the condition with both SO2 and Cl- / F- contamination in the solvent. In this paper, pitting risk of stainless steels under wet SO2 environments with Cl- and F- in high temperature and high pressure conditions was investigated. Cyclic polarization measurements were used to illustrate the corrosion and passive behavior of the stainless steels under the tail gas conditions. Electrochemical behavior of stainless steels in SO2-saturated solutions with various concentrations of Cl- and F- was also studied.INTRODUCTIONWith increasing concerns of air pollution, the emission of sulfur from industries in the forms of SOx has been closely monitored and regulated by many countries. The reduction of sulfur dioxide (SO2) emission from the flue gases of fossil fuel-fired power plants has become one of the most urgent environmental issues for the sustainable society 1-5. Meanwhile, once dissolved in the solution, SO2 can be corrosive to materials. The researchers found that the effect of SO2 would be more moderate in comparison with those of contaminants such as HCl, HNO3, and SO3, which would exert a significant effect on the aqueous phase pH even in small concentrations 6. SO2, which has a high solubility in H2O, results in the formation of H2SO3 and consequently lowers the pH (~2) of the aqueous phase 6.In SO2 saturated solutions, carbon steels may suffer high corrosion rates. Therefore, corrosion Resistant Alloys (CRAs) are widely used in SO2 conditions to meet the requirement for materials. However, the CRAs may also suffer corrosion, especially pitting and stress corrosion cracking in Cl- / F- condition 7-11. This paper focused on the effect of F- and Cl- on the corrosion behavior of stainless steels. Different concentrations of F- and Cl- were selected to investigate their effect. Additionally, the materials selection of stainless steels under low and high Cl/F containing conditions was also studied.
ABSTRACTThis paper presents the results of an investigation into the effect of ppm concentrations of acetic acid on the electrochemical corrosion behavior of API 5L X65 carbon steel in a sour environment. Electrochemical techniques, Linear Polarization Resistance (LPR), Potentiodynamic Polarization and Electrochemical Impedance Spectroscopy (EIS), were used to characterize the electrochemical behavior of API 5L X65 carbon steel in a 3.5 wt% NaCl solution with 10 ppm of hydrogen sulfide (H2S) and acetic acid at 0, 100, 500 and 1000 ppm concentrations. All tests were conducted at 40°C temperature and 1.0 bar CO2 pressure.The corrosion product film formed on the electrode surface is less protective in the presence of acetic acid than when acetic acid was not present. This is confirmed by a decrease in the polarization resistance and increase in the corrosion rates with increase in acetic acid concentration. EIS shows high impedance of the film with no acetic acid present, indicating a highly protective corrosion product on the electrode surface. However, the impedance significantly decreases as the acetic acid concentration increases. Examination of the tested electrodes in solutions containing acetic acid shows pitting corrosion on the surface. This appears to be due to the dissolution of iron acetate from the corrosion product scale.INTRODUCTIONThe effect of acetic acid on CO2 corrosion has been studied in the literature.1-4 Experimental work has also been done on the effect of small amounts of H2S on CO2 corrosion of carbon steel, and the different chemical and electrochemical reactions involved in CO2/H2S corrosion process in the presence of acetic acid. 5-7These studies found that the presence of small amounts of H2S results in a rapid and significant reduction of the CO2 corrosion rate. The reduction of the corrosion rate is usually associated with the formation of a corrosion product film on the metal surface, even if the bulk conditions for super saturation of FeCO3 or FeS are not met. Analysis of the corrosion product film usually shows the presence of a very thin mackinawite film. It has been reported that the process of FeS film formation is linked to a solid state reaction where hydrogen sulfide (or sulfide ions) reacts directly with the iron at the metal surface.6 The chemistry of iron sulfide film formation is very complex. It was reported in a review paper that there are three main forms of FeS commonly found in the field: Mackinawite, Pyrrhotite and Pyrite.8
Käfer, Sven (Technische Universität Darmstadt Research Group for System Reliability) | Melz, Tobias (Technische Universität Darmstadt Research Group for System Reliability) | Kaufmann, Heinz (Fraunhofer Institute for Structural Durability and System Reliability LBF) | Engler, Christopher Tom (Technische Universität Darmstadt State Material Testing Institute and Institute for Materials Technology) | Anderson, Georg (Technische Universität Darmstadt State Material Testing Institute and Institute for Materials Technology) | Oechsner, Matthias (Technische Universität Darmstadt State Material Testing Institute and Institute for Materials Technology)
ABSTRACTEngine components, such as injection systems, encounter a large number of load cycles (N > 107) during their lifetime and are exposed to potentially corrosive media such as fossil fuels. For this reason, corrosion fatigue in the very high cycle fatigue (VHCF) regime has to be taken into account for reliable fatigue design. To reduce carbon dioxide (CO2) emission, fossil fuels are blended with biogenic components. Biofuels are potentially more corrosive than unblended fuels due to the hygroscopic properties, e.g. ethanol, which is added to gasoline fuels.There is not much known about the corrosion fatigue behavior of high-strength chromium steels in bio-fuels, yet. Indeed investigations show that biofuels reduce the number of load cycles to failure of engine components significantly . Therefore, it is essential to investigate the corrosive impact of fuels with biogenic components by performing corrosion fatigue tests. In the current paper, the impact of corrosion fatigue was investigated on notched and unnotched specimens of stainless 17% chromium steel 1.4016 (X6Cr17), AISI 430 in air and E85 biofuel (gasoline fuel with 85% ethanol added). The results were obtained at a stress ratio of R = 0 with different testing rigs to investigate the influence of testing frequencies (f = 20, 150Hz). The test results represent the basis for a concept that will be able to estimate the impact of corrosion fatigue in the VHCF region.INTRODUCTIONThe amount of renewable sources shall be increased to 10% in biofuels according to the directive 2009/28/EC  to reduce the greenhouse gas emissions in 2020 by 6% . During the implementation of E10 biofuel, many consumers have been averse to biofuels, because of the lack of long-term studies in conventional combustion engines . Due to the higher amount of ethanol, the hygroscopic properties of biofuels increase causing an input of different kinds of corrosive substances, e.g. chlorides that are dissolved in water. High alloyed Cr-steels that are used in engine components form passive layers protecting the core material from further corrosion. High chloride contents superimposed by mechanical load can locally damage these passive layers resulting in pitting and possibly intergranular corrosion. These effects have a major impact on the fatigue strength of the materials . The corrosive impact occurs most of the time at the high stressed part of engine components at the surface. This results in a superimposed crack initiation and crack propagation. Therefore, corrosive fatigue tests results are of great interest for such components. Regarding the downsizing trend of the automotive industry by reducing fuel consumption and simultaneously increasing the engine power in terms of material optimization, it is indispensable to consider the effect of corrosion already in an early stage of development. For this reason, corrosion fatigue effects have also to be taken into account during the design process of engine components such as fuel pumps, the fuel distributors, and high-pressure injection valves  by choosing the right material and the right design.